Electric power circuit breaker equipped with a latching mechanism wherein restoring forces are provided as a function of switching shaft position

ABSTRACT

An electric power circuit breaker is disclosed wherein the latching mechanism as well as other parts which affect the motion of the contacts are returned by restoring forces to their initial position after the breaker is opened. The restoring forces are made ready in dependence on the position of the switching shaft of the breaker and are smaller in the closed position of the switching shaft than in the open position thereof. The invention is suited particularly for low-voltage power circuit breakers for high rated currents wherein the economic configuration of the required springs is of importance.

United States Patent 1191 Preuss 1 Sept. 10, 1974 [5 1 ELECTRIC POWERCIRCUIT BREAKER 3,098,134 7/1963 Nijland 200/153 H EQUIPPED WITH ALATCHING 3,600,541 8/1971 Goodwin, Jr. 200/153 G MECHANISM WHEREINRESTORING FORCES ARE PROVIDED AS A FUNCTION OF SWITCHING SHAFT POSITIONInventor: Bernhard Preuss, Berlin, Germany Siemens Aktiengesellschaft,Munich, Germany Filed: Apr. 18, 1973 App]. No.: 352,202

Assignee:

Foreign Application Priority Data Apr. 19, 1972 Germany 2219892 PrimaryExaminer-Robert K. Schaffer Assistant Examiner-Gerald P. Tolin Attorney,Agent, or Firm-Kenyon & Kenyon Rielly Carr & Chapin An electric powercircuit breaker is disclosed wherein the latching mechanism as well asother parts which affect the motion of the contacts are returned byrestoring forces to their initial position after the breaker is opened.The restoring forces are made ready in dependence on the position of theswitching shaft of the breaker and are smaller in the closed position ofthe switching shaft than in the open position thereof. The invention issuited particularly for low-voltage power circuit breakers for highrated currents wherein the economic configuration of the requiredsprings is of importance.

ABSTRACT 8 Claims,- 3 Drawing Figures ELECTRIC POWER CIRCUIT BREAKEREQUIPPED WITH A LATCHING MECHANISM WHEREIN RESTORING FORCES ARE PROVIDEDAS A FUNCTION OF SWITCHING SHAFT POSITION BACKGROUND OF THE INVENTIONElectric power circuit breakers can be equipped with a latchingmechanism which serves in particular for mechanical latching andtripping as well as trip-free releasing the contact members andeffecting force transformation when switching the breaker to the closedposition. These functions are realized by lever arrangements, clutches,linkages, cams or similar members. These members can occupy two mainpositions, namely, for the closed position and the open position of thecontact members of the circuit breaker.

If a power circuit breaker is to be reclosed after opening, certainparts of the latching mechanism must first be returned to their initialposition in preparation for the breaker closing operation. A latchinglever, for instance, must be returned from the released position to thelatched position. In conventional arrangements, this is achieved bymeans of auxiliary forces which are supplied, for example, by means ofsuitable springsor by means of a reversible motor drive. In thisconnection, reference may be had to the German publication:Starkstromtechnik, Vol. II, 8th ed., 1960, Verlag Wilh. Ernst & Sohn,pp. 188 to 190.

SUMMARY OF THE INVENTION The invention is based on an electric powercircuit.

breaker provided particularly for low voltage. The circuit breakerincludes a drive mechanism and a latching mechanism containing aswitching shaft as well as a latching lever which can be released by atripping device. Also provided are additional members which can bereturned to their initial position by restoring forces after the breakeropens.

It is an object of the invention to provide an electric power circuitbreaker which achieves an improved balance of forces of the latchingmechanism which makes possible, in particular, energy storage devices ofmore economical construction for closing and opening the power circuitbreaker.

According to the invention, the restoring forces are made available independence on the position of the switching shaft and are smaller in theclosed position of the switching shaft than in the open position. Thismakes it unnecessary for the restoring forces for the latching lever andother members of the latching mechanism to act continuously; instead,these forces are provided only when they are needed. As a consequence,the breaker opening spring required for opening the contacts of thepower circuit breaker, for instance, can be made weaker than would bepossible if the return spring of the latching lever in the latchingmechanism were fully effective continuously. A delay in switching openis thereby avoided at the same time.

The electric power circuit breaker of the invention includes as afeature contact means switchable between open and closed positions; alatching mechanism for actuating the contact means; and a drivemechanism operatively connected to the latching mechanism for initiatingthe closing of the contact means by the latching mechanism. The latchingmechanism includes a switching shaft operatively connected to thecontact means and rotatable between first and second positionscorresponding to the open and closed positions of the contactsrespectively. Lever means is provided as part of the latching mechanismand is responsive to the drive mechanism for rotating the switchingshaft from the first position to the second position. The lever meanshas a plurality of interacting lever parts movable between an initialposition and an end position corresponding respectively to the first andsecond positions of the switching shaft. A latching lever coacts withthe lever means to hold the switching shaft in the second position andtripping means releasably engages the latching lever for releasing thelatching lever to withdraw the hold on the lever means. Breaker openingmeans is operatively connected to the shaft for moving the shaft fromthe second position to the first position when the latching lever isrealeased by the tripping means. The latching mechanism further includesa first resilient means connected to the lever means for directing atleast a portion of the interacting parts to the initial position by theaction of a restoring force developed in the first resilient means inresponse to the movement of the switching shaft from the second positionto the first position, and a second resilient means engages the latchinglever and develops a restoring force for returning the latching lever tothe tripping means in response to the movement of the shaft from thesecond position to the first position whereby the magnitude of therestoring force developed by the second resilient means is less when theshaft is in the second position than when the shaft is in the firstposition.

The invention can, for instance, be realized in a form that in a powercircuit breaker which includes a switching lever rigidly connected withthe switching shaft, the switching lever serves as an anchor for areturn spring. The return spring is tensioned only when the switchingshaft with the switching lever arrives in the open position. If, forinstance, a latching lever is provided which is pivoted at one end andcooperates at its other end-with a tripping shaft, the switching levermay be connected articulately with a bending spring which is bracedagainst a fixed anchor point and a stop of the latching lever and whichdevelops a bending stress that increases as the switching lever movesinto the open position. This bending spring may consist of spring wirefor example.

Thus, according to another feature of the invention, one of theinteracting parts of the lever means is a switching lever rigidlymounted on the switching shaft. The first resilient means can be a firstspring having one end anchored to the switching lever, and the secondresilient means can be a second spring also anchored to the switchinglever.

Still another feature of the invention provides that the latching leverbe pivotally mounted'at one end thereof and have a bracing stop disposedthereon for bracing the second spring. The tripping means can be atripping shaft releasably engaging the other end of the latching lever.The latching mechanism can include stationary anchor means for bracingthe second spring and the second spring is a bending spring articulatelyjoined to the switching lever and drawn about the bracing stop toincrease the bending stress in the bending spring as .the switchinglever moves with the switching shaft from the second position to thefirst position. According to a subsidiary feature, the bending springconsists of spring wire.

The invention can also be used for returning members of the latchingmechanism which serve to transmit the closing force. It is, for example,suited for power circuit breakers wherein the force is transmitted tothe switching shaft via an idler lever pivotally mounted on theswitching shaft and a coupling member arranged between the idler leverand the switching lever. In a further embodiment of the invention, theone lever of an elbow lever system can be articulately connected to theidler lever, and a tension spring can be arranged between the otherlever of the elbow lever system and the switching lever. The points ofconnection of the spring is chosen so that the spacing therebetween isessentially maintained during the breaker closing operation. Norestoring force of the elbow lever system must therefore be overcome.when the breaker is closed. The tension spring is tensioned only whenthe breaker opens whereby the restoring force is made available.

According to another feature of the invention, the first resilient meansis a tension spring and one of the lever parts of the lever means is aswitching lever rigidly mounted on the switching shaft. An other one ofthe lever parts is an idler lever pivotally mounted on the switchingshaft and a further one of the lever parts is a coupling lever arrangedbetween the switching lever and the idler lever. A still further one ofthe lever parts is an elbow lever made up of two lever arms pivotallyconnected to each other. One of the lever arms of the elbow lever isarticulately joined to the idler lever. The switching lever and theother one of the lever arms of the elbow lever have respective springmounts disposed thereon so as to maintain an approximately constantspacing therebetween as the switching shaft is rotated from the firstposition to the second position, the tension spring being arrangedbetween the spring mounts.

Although the invention is illustrated and described herein as anelectric power circuit breaker equipped with a latching mechanism, it isnevertheless not intended to be limited to the details shown, sincevarious modifications may be made therein within the scope and the rangeof the claims. The invention, however, together with additional objectsand advantages will be best understood from the following descriptionand in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of apower circuit breaker for low voltage according to the invention. Thediagram shows essentialelements of the latching mechanism and the drivemechanism of the power circuit breaker.

FIG. 2 is a detailed schematic diagram of the latching mechanism shownseparately in an enlarged scale. The latching mechanism is in its openposition with the latching lever locked.

FIG. 3 shows a schematic diagram similar to FIG. 2 and shows thelatching mechanism in two different positions, namely. at the start andat the end of the breaker opening operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring toFIG. 1, a power circuit breaker 1 is shown which is equipped with adrive mechanism 2.

The current path of the power circuit breaker 1 includes an upperterminal block 3 and a stationary contact 4 rigidly connected therewith.A movable contact 5 is disposed opposite contact 4. A bendable conductorsection 7 is arranged between the contact 5 and a lower terminal block6. Between the fixed contact 4 and the movable contact 5 are situatedparallel conductor sections 10 andv 11, which for high currents cause anincrease of the contact pressure between the contacts 4 and 5.

The latching mechanism of .the power circuit breaker 1 which is shown inFIG. 1 includes a switching shaft 12 with a two-arm lever 13 having alever arm 14 connected with an elbow lever system which in its entiretyis designated by reference numeral 15 and having another lever arm 16engaging the movable contact 5 by means of a lever 17. A link 20 servesto guide the movable contact 5. The movable contact 5 and the conductorsection 11 connected therewith is further engaged by a spring 21 whichgenerates the contact pressure in the closed breaker position and alsoopens the movable contact when the breaker is switched open. The elbowlever system 15 is braced with the one elbow lever 22 against aninterlock device 23. The interlock device 23 comprises a latching lever24, a latching pawl 25 and a return spring 26 for the latching pawl 25.

The drive mechanism 2 connected with the power circuit breaker 1includes a torsion rod spring 30 which is clamped at one end in asupport 31. The torsion rod spring 30 carries a cam 32 at its front end.A projection 33 of the cam 32 can be engaged by a dog 34 which isfastened on a shaft 35 upon which a hand lever 36 acts. The torsion rodspring 30 may be a solid member, but preferably, it is made up of astack of individual leaf springs.

In FIG. 1, the hand lever 36 is shown in a position just before reachingthe closed position indicated by the broken line 37. If the hand lever36 is moved still further, the dog 34 slides off the projection 33 andreleases the cam 32. The cam 32 rotates counterclockwise and pressesagainst a roller 18 arranged at the joint of the elbow lever system 15until the elbow lever system 15 goes past its dead center position andthe elbow lever 22 comes to rest against a stop 28. The described motionof the elbow lever system 15 causes a clockwise rotation of theswitching shaft 12 and therefore the closing of the power circuitbreaker 1.

If the power circuit breaker l is to be switched open, the latching pawl25 is pulled off the latching lever 24 in the direction of the arrow 29.The support of the elbow lever system 15 is thereby withdrawn, and thespring 21 pulls the movable contact 5 into the position shown in FIG. 1.

In the following, the construction and operation of the latchingmechanism will be described in detail. In FIGS. 2 and 3, the switchingshaft 40 corresponds to the switching shaft 12 shown in FIG. 1. Thelevers 42 and 43 form the elbow lever system designated by referencenumeral 15 in FIG. 1. The lever 43 is pivotally mounted on a stationarybearing post 44 and has an extension 45 which projects out beyond thepivot post 44 and which in the, open position of the breaker accordingto FIG. 2 rests against a stop 48. The other lever 42 is linked with anidler lever 47 by means of a further pivot pin 49. The idler lever 47 ismounted on the switching shaft 40'and has a working surface 50 whichcoacts with a roller 52 of a roller lever 51. The roller lever 51 issupported by means of a pivot pin 53 on a switching lever 54 which isrigidly connected with the control shaft 40. On the roller lever 51, afurther roller 55 is provided and is guided on a circular track 57 of alatching lever 56. The latching lever 56 is of approximatelysickle-shaped configuration and is pivotally mounted at its one endabout a pin 60. At its other end, the latching lever 56 has a nose 62which, in the closed position, rests against a tripping shaft 63. Afixed stop 68 limits the travel of the latching lever 56 when thebreaker switches to the open position.

At the end of the switching lever 54 there is an opening 61 wherein along bendable spring 65 is engaged. The spring 65 is guided between thestationary stops 66 and 67 and coacts with a stop 70 of the latchinglever 56, the stop 70 being in the region of the circular track 57.

The switching lever 54 further has a rear extension 71 at which a pin 73is arranged as the anchor for a tension spring 72. With its other end,the tension spring 72 engages the anchor point 74 of the extension 45 ofthe elbow lever 43.

If a force acts on the elbow lever joint 41 of the elbow levers 42 and43 as already explained in connection with FIG. 1, the idler lever 47 isswung counterclockwise as the elbow levers 42 and 43 stretch out to agreater extent and the roller lever 51 with its roller 55 is thereby ledalong the circular track 57 of the latching lever 56. The switchinglever 54 and the switching shaft 40 are likewise taken along in acounterclockwise direction. With this movement the breaker enters itsclosed position (depicted by solid lines in FIG. 3) where the lever 43rests against a stop 46 and is in a position beyond the dead centerpositionv In this breaker closing operation, the rear extension 71 ofthe switching lever 54 and the extension 45 of the lever 43 are movingin the same direction, so that the spacing of the anchor points 73 and74 of the tension spring 72 remains practically unchanged. The tensionspring 72 is therefore not tensioned.

To switch the breaker to the open position, the nose 62 of the latchinglever 56 is released by rotating the tripping shaft 63. The latchinglever 56 thereby assumes the position shown by solid lines in FIG. 3. Inthis movement, the roller 52 of the roller lever 51 slides off theworking surface 50 of the idler lever 47 and the switching lever 54 withthe switching shaft 40 rotate to arrive in the open position under theinfluence of the stored breaker opening force as shown by the brokenlinecontour in FIG. 3.

The point of application of the bending spring 65 on the switching lever54 moves along a circular line during the opening operation which hasthe consequence that the bending spring 65 lies against the stop 70 ofthe latching lever 56 and is bent in such a manner that a re storingforce is exerted on the latching lever 56. A comparison of FIGS. 2 and 3shows that the bending stress in the open position is greater than inthe closed positlon.

FIG. 3 shows furthermore that the movement of the switching lever 54from the closed position to the open position is accompanied by atensioning of the tension spring 72 thereby making available therestoring force which is necessary to bring the elbow levers 42 and 43into the position corresponding to FIG. 1.

Because of the fact that the tension spring 72 is not tensioned in thebreaker closing operation, the drive mechanism of the power circuitbreaker need not overcome additional forces in closing. Similarly, thebreaker opening spring need not overcome any additional forces duringthe opening operation because the bending spring 65 is largely relaxed.This results not only in a favorable balance of forces, but also inparticularly rapid tripping. I

What is claimed is:

1. An electric power circuit breaker comprising contact means switchablebetween open and closed positions; a latching mechanism for actuatingsaid contact means; and a drive mechanism operatively connected to saidlatching mechanism for initiating the closing of said contact means bysaid latching mechanism; said latching mechanism including: a switchingshaft operatively connected to said contact means and rotatable betweenfirst and second positions corresponding to said open and closedpositions of said contact means respectively, lever means responsive tosaid drive mechanism for rotating said switching shaft from said firstposition to said second position, said lever means having a plurality ofinteracting lever parts movable between an initial position and an endposition corresponding respectively to said first and second positionsof said shaft, a latching lever coacting with said lever means to holdsaid switching shaft in said second position, tripping means releasablyengaging said latching lever for releasing said latching lever towithdraw said hold on said lever means, breaker opening meansoperatively connected to said shaft for moving said shaft from saidsecond position to said first position when said latching lever isreleased by said tripping means, first resilient means connected to saidlever means for directing at least a portion of said interacting partsto said initial position by the action of a resilient restoring forcedeveloped in said first resilient means only in response to the movementof said shaft from said second position to said first position wherebythe force developed by said drive mechanism acting upon said lever meansis unopposed by the resilient force of said first resilient means whensaid switching shaft is rotated from said first position to said secondposition, and second resilient means engaging said latching lever so asto be largely relaxed when said shaft is in said second position and todevelop a restoring force for returning said latching lever to saidtripping means in response to the movement of said shaft from saidsecond position to said first position whereby the magnitude of saidrestoring force developed by said second resilient means is less whensaid shaft is in said second position than when said shaft is in saidfirst position.

2. The electric power circuit breaker of claim 1, one of saidinteracting parts of said lever means being a switching lever rigidlymounted on said switching shaft, said first resilient means being afirst spring having one end anchored to said switching lever, and saidsecond resilient means being a second spring also anchored to saidswitching lever.

3. The electric power circuit breaker of claim 2, said latching leverbeing pivotally mounted at one end thereof and having a bracing stopdisposed thereon for bracing said second spring, said tripping meansbeing a tripping shaft releasably engaging the other end of saidlatching lever, said latching mechanism including stationary anchormeans for bracing said second spring. said second spring being a bendingspring articulately joined to said switching lever and drawn about saidbracing stop to increase the bending stress in said bending spring assaid switching lever moves with said switching shaft from said secondposition to said first position.

4. The electric power circuit breaker of claim 3, said bending springconsisting of spring wire.

5. The electric power circuit breaker of claim I, said first resilientmeans being a tension spring, one of said lever parts of said levermeans being a switching lever rigidly mounted on said switching shaft,an other one of said lever parts being an idler lever pivotally mountedon said switching shaft, a further one of said lever parts being acoupling lever arranged between said switching lever and said idlerlever, a still further one of said lever parts being an elbow levercomprising two lever arms pivotally connected to each other, one of saidlever arms of said elbow lever being articulately joined to said idlerlever, said switching lever and said other one of said lever arms ofsaid elbow lever having respective spring mounts disposed thereon so asto maintain an approximately constant spacing therebetween as saidswitching shaft is rotated from said first position to said secondposition, said tension spring being arranged between said spring mounts.

6. The electric power circuit breaker of claim 5, said drive mechanismincluding force generating means arranged with respect to said elbowlever of said latching mechanism for imparting a force thereto wherebysaid elbow lever coacts with said idler lever, said coupling lever andsaid switching lever to transmit said force to said switching shaft.

7. The electric power circuit breaker of claim 6, said second resilientmeans being a bending spring, said latching lever being pivotallymounted at one end thereof and having a bracing stop disposed thereonfor bracing said bending spring, said tripping means being a trippingshaft releasably engaging the other end of said latching lever, saidlatching mechanism including stationary anchor means for bracing saidbending spring, said bending spring being articulately joined to saidswitching lever and drawn about said bracing stop to increase thebending stress in said bending spring as said switching lever moves withsaid switching shaft from said second position to said first position.

8. The electric power circuit breaker of claim 7, said bending springconsisting of spring wire.

1. An electric power circuit breaker comprising contact means switchablebetween open and closed positions; a latching mechanism for actuatingsaid contact means; and a drive mechanism operatively connected to saidlatching mechanism for initiating the closing of said contact means bysaid latching mechanism; said latching mechanism including: a switchingshaft operatively connected to said contact means and rotatable betweenfirst and second positions corresponding to said open and closedpositions of said contact means respectively, lever means responsive tosaid drive mechanism for rotating said switching shaft from said firstposition to said second position, said lever means having a plurality ofinteracting lever parts movable between an initial position and an endposition corresponding respectively to said first and second positionsof said shaft, a latching lever coacting with said lever means to holdsaid switching shaft in said second position, tripping means releasablyengaging said latching lever for releasing said latching lever towithdraw said hold on said lever means, breaker opening meansoperatively connected to said shaft for moving said shaft from saidsecond position to said first position when said latching lever isreleased by said tripping means, first resilient means connected to saidlever means for directing at least a portion of said interacting partsto said initial position by the action of a resilient restoring forcedeveloped in said first resilient means only in response to thE movementof said shaft from said second position to said first position wherebythe force developed by said drive mechanism acting upon said lever meansis unopposed by the resilient force of said first resilient means whensaid switching shaft is rotated from said first position to said secondposition, and second resilient means engaging said latching lever so asto be largely relaxed when said shaft is in said second position and todevelop a restoring force for returning said latching lever to saidtripping means in response to the movement of said shaft from saidsecond position to said first position whereby the magnitude of saidrestoring force developed by said second resilient means is less whensaid shaft is in said second position than when said shaft is in saidfirst position.
 2. The electric power circuit breaker of claim 1, one ofsaid interacting parts of said lever means being a switching leverrigidly mounted on said switching shaft, said first resilient meansbeing a first spring having one end anchored to said switching lever,and said second resilient means being a second spring also anchored tosaid switching lever.
 3. The electric power circuit breaker of claim 2,said latching lever being pivotally mounted at one end thereof andhaving a bracing stop disposed thereon for bracing said second spring,said tripping means being a tripping shaft releasably engaging the otherend of said latching lever, said latching mechanism including stationaryanchor means for bracing said second spring, said second spring being abending spring articulately joined to said switching lever and drawnabout said bracing stop to increase the bending stress in said bendingspring as said switching lever moves with said switching shaft from saidsecond position to said first position.
 4. The electric power circuitbreaker of claim 3, said bending spring consisting of spring wire. 5.The electric power circuit breaker of claim 1, said first resilientmeans being a tension spring, one of said lever parts of said levermeans being a switching lever rigidly mounted on said switching shaft,an other one of said lever parts being an idler lever pivotally mountedon said switching shaft, a further one of said lever parts being acoupling lever arranged between said switching lever and said idlerlever, a still further one of said lever parts being an elbow levercomprising two lever arms pivotally connected to each other, one of saidlever arms of said elbow lever being articulately joined to said idlerlever, said switching lever and said other one of said lever arms ofsaid elbow lever having respective spring mounts disposed thereon so asto maintain an approximately constant spacing therebetween as saidswitching shaft is rotated from said first position to said secondposition, said tension spring being arranged between said spring mounts.6. The electric power circuit breaker of claim 5, said drive mechanismincluding force generating means arranged with respect to said elbowlever of said latching mechanism for imparting a force thereto wherebysaid elbow lever coacts with said idler lever, said coupling lever andsaid switching lever to transmit said force to said switching shaft. 7.The electric power circuit breaker of claim 6, said second resilientmeans being a bending spring, said latching lever being pivotallymounted at one end thereof and having a bracing stop disposed thereonfor bracing said bending spring, said tripping means being a trippingshaft releasably engaging the other end of said latching lever, saidlatching mechanism including stationary anchor means for bracing saidbending spring, said bending spring being articulately joined to saidswitching lever and drawn about said bracing stop to increase thebending stress in said bending spring as said switching lever moves withsaid switching shaft from said second position to said first position.8. The electric power circuit breaker of claim 7, said bending springconsisting of spring wire.